Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$49.77	12.817%	$56.149	$56.15	$56.15	$56.10
Purchase #2	$93.78	6.615%	$99.9835	$99.98	$100.00	$100.00
Purchase #3	$68.27	5.527%	$72.0433	$72.04	$72.05	$72.00
Purchase #4	$56.69	9.425%	$62.033	$62.03	$62.05	$62.00
Purchase #5	$185.47	13.310%	$210.1561	$210.16	$210.15	$210.20
Purchase #6	$128.74	9.604%	$141.1042	$141.10	$141.10	$141.10
Purchase #7	$247.77	4.226%	$258.2408	$258.24	$258.25	$258.20
7 purchase totals =	$830.49		$899.7099	$899.70	$899.75	$899.60